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FOUS30 KWBC 031628
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1228 PM EDT Fri May 3 2024

Day 1
Valid 16Z Fri May 03 2024 - 12Z Sat May 04 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
SOUTHEAST TEXAS...

...16Z Update (Delayed)...

...Southeast Texas...

In coordination with HGX/Houston, TX; LCH/Lake Charles, LA; and
FWD/Fort Worth, TX forecast offices, a Moderate Risk upgrade was
included with this update for portions of southeast Texas.
Persistent backbuilding storms producing 1-2 inches per hour
rainfall rates has been occurring over areas that have been
pushing a foot of new rain over the past 48 hours. For more details
please see the corresponding MPD 214 at
www.wpc.ncep.noaa.gov/metwatch/metwatch_mpd_multi.php?md=0214&yr=2024.

...Arklatex...

Another bigger change made with this update was to trim down the
inherited Slight out of the Arklatex region, confining it to the
extremely hard hit southeast Texas, and into southwest Louisiana.
The ongoing MCS at the time of this writing over eastern Arkansas
and northern Louisiana is weakening and breaking into component
convection. While those stronger storms will likely hang on a bit
longer, the increasingly isolated nature of the convection suggests
that any potential resultant flash flooding will be isolated, and
more indicative of a Marginal. Further, once the MCS weakens,
dissipates and pushes east into Mississippi, guidance is in good
agreement that that will be the end of the day`s (and tonight`s)
rain for that area. Of course, there`s always potential in this
very moisture-rich environment that popup convection could
redevelop, but without much CAMs indication of that, that too
suggests the flash flooding threat is waning.

...Central Plains...

The Marginal Risk area in Kansas has been expanded a bit to the
south in deference to the newest 12Z HRRR suggesting a line of
convection will develop this afternoon and tonight over the heart
of the state. This in turn would limit development further north
across Nebraska. Once again the CAMs have been performing poorly so
the Marginal area is really a hedge to cover the wide range of
possibilities of convective evolution. For Kansas, the
southwestern part of the state remains very dry as far as soil
moisture conditions are concerned, so the Marginal was to cover
potential training convection.

Further south into Oklahoma, guidance has been trending downward
for most of the state, so the Marginal was removed with this
update. Dry line convection likely across west Texas may sneak
across the Red River into Oklahoma, so that potential will need to
continue to be monitored.

...Central Appalachians...

Shower activity from Tennessee to Ohio may develop into more
robust, albeit scattered convection across the Marginal Risk area
this afternoon and evening. Soils are still a bit sensitive here,
but the rainfall is not expected to be notable, so the Marginal
covers the isolated flash flooding risk here.

Wegman



Day 2
Valid 12Z Sat May 04 2024 - 12Z Sun May 05 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
WESTERN AND SOUTHERN HIGH PLAINS...

Height falls aloft ejecting eastward from the Southern Rockies and
the presence of a dryline over West Texas will foster an
environment for thunderstorms capable of producing heavy rainfall
by later in the day on Saturday that persists into Saturday
night/early Sunday morning. Precipitable water values will have
increased to nearly 1,5 inches...some 2 to 2.5 standardized
anomalies greater than climatology...over portions of central and
west central Texas by 00Z Sunday in response to a period of
southeasterly flow off of the Gulf of Mexico. Consensus of model
guidance QPF in the range of 1 to 3 inches seems
reasonable...although the UKMET was a notable outlier.

...Northern Sierra Nevada Foothills...

A fairly robust IVT pulse will slide down the west coast with
southwesterly flow aimed orthogonally to the northern and central
Sierra`s by Saturday. Higher elevations will be greeted with more
snow, but the adjacent foothills will remain warm enough to benefit
from all rainfall. Rates will be borderline overall, but the
prospects for over 1" of precip has grown in the past succession
of runs with the ensemble bias corrected guidance now upwards of 2"
now forecast within the elevations below 8000` MSL, falling mainly
in a span of 8-12 hours. The threat is on the lower end of MRGL. Maintained
continuity from previous forecast and will assess whether it needs
adjusting, or removal pending future trends in guidance.

Bann

Day 3
Valid 12Z Sun May 05 2024 - 12Z Mon May 06 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE SOUTHERN
PLAINS...

The potential for excessive rainfall makes its way eastward on
Sunday in association with a closed low aloft and a cold front at
the surface. Model QPF was not as heavy as forecast on Day 2 as
shifting low level flow results in weaker low level moisture flux
convergence along the front. Despite model QPF generally being 2
inches or less...opted for a Slight Risk given the wet antecedent
conditions over portions of eastern Texas and eastern Oklahoma.

Bann


Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt